Phyla Platyhelminthes and Nemertina 405 



dermal cells is a thin layer of elastic tissue known as the elastic base- 

 ment membrane. Interior to this are the muscle layers; circular, 

 longitudinal, diagonal, and dorsoventral fibers can be seen. All spaces 

 between organs are filled with loose connective tissue or parenchyma. 



pharynx 



buccal cavity opening of pharynx 



brain 



eyespot 



enteron 



pharynx 



mouth 



lateral nerve cord 



testes 



opening of pharynx 



sperm ,duct 



semmal vesicle 

 I 

 I penis 



commissure 



genital pore 



ovary 



oviduct yolk gland copulatory sac 



genital chamber 



excretory pore 



flame cells 



excretory pore 



Fig. 133. — The organ systems of a planarian. A, The digestive system; B, the 

 nervous system; C, the reproductive system, including both male and female or- 

 gans; D, the excretory system. (From Guyer: Animal Biology, Harper & Brothers.) 



